Masking techniques for metal plating

ABSTRACT

Apparatus for metal plating an article comprising a frame having a plurality of sealing members positioned thereon, the frame being capable of conducting an electrical current between sealing members, each sealing member being adapted to be in close contact with part of an article to be located thereon, and to thereby substantially prevent fluid from touching that part of the article or entering into a bore or recess of the article, each sealing member further being adapted to conduct current between the frame and the article.

[0001] The present invention relates to the field of metal plating ofarticles, and in particular to masking articles, including those havinga recess or bore therein.

[0002] In the manufacturing industry, it is often considered desirableto metal plate articles, that is to cover articles with a thin layer ofmetal, so that the article becomes stronger, more durable and corrosionresistant. This method of metal plating may be achieved byelectroplating for example, where an article is immersed in a metallicsolution and subjected to an electric current. Such a metal platingtechnique generally results in the whole of the article being plated inmetal, which may be undesirable, for example, where the article has abore or a recess. Often it is desirable to coat just the outer areas ofthe article whilst leaving the recess or bore untreated. This is usuallyachieved by masking the recess or bore such that the metal is preventedfrom adhering to that part of the article.

[0003] A known method of masking recesses or bores is to coat the recessor bore with a non-conductive lacquer to which the metal is unable toadhere. The lacquer is generally applied to the recess or bore manuallyusing a brush. Before the metal plating process is undertaken, thelacquer is allowed to dry and any excess lacquer is removed.

[0004] This method of masking, however, is time consuming, very labourintensive, and messy. Additionally, following the metal plating process,the lacquer must then be removed from the article by immersion in adegreaser, which uses trichloroethlene and which has health and safetyimplications and environmental implications due to solvent emissions.

[0005] The present invention seeks to overcome the disadvantages of thepresent masking method, and seeks to provide a quicker, cleaner and lesslabour intensive method of metal plating an article including thosehaving a recess or bore therein.

[0006] According to the present invention there is provided a framehaving a plurality of sealing members positioned thereon, the framebeing capable of conducting an electrical current between sealingmembers, each sealing member being adapted to be in close contact withpart of an article to be located thereon and to thereby substantiallyprevent fluid from touching that part of the article or entering into abore or recess of the article, each sealing member further being adaptedto conduct current between the frame and the article.

[0007] A force exerting device is advantageously provided on the framefor exerting the force on the article to hold the article firmly inclose contact with a sealing member.

[0008] The force exerting device preferably comprises a resilientlybiased member.

[0009] The sealing members may be substantially planar. Alternativelysealing members may be adapted to extend at least part way into a recessor bore of the article to be located thereon.

[0010] The frame exerting device may be adapted to hold the articlebetween two sealing members. Alternatively the force exerting device maybe adapted to hold the article between the force exerting device and asealing member.

[0011] The sealing members may be substantially spherical orhemi-spherical. Alternatively the sealing members may be frusto-conical.The sealing members may be formed from titanium.

[0012] Alternatively the sealing members may comprise an electricallyconductive core substantially encased in an electrical insulatormaterial such as steel encased in plastic, for example. Alternativelythe sealing members may be formed from a compressible, non-conductivematerial.

[0013] An electrically conductive member, such as a wire or spring forexample, may extend from the frame through a sealing member such thatthe electrically conductive member is capable of forming an electricalcontact between an article located on the sealing member, and the frame.The frame is preferably coated in a non-conductive material to preventthe frame from becoming metal plated when a current is applied to theframe and it is exposed to a metallic solution.

[0014] According to the present invention there is further provided aframe having a plurality of sealing members positioned thereon, theframe being capable of conducting an electrical current between sealingmembers, each sealing member being adapted to extend at least part wayinto a recess or bore of an article to be located thereon and tosubstantially prevent fluid from entering into the bore or recess of thearticle, each sealing member further being adapted to conduct currentbetween the frame and the article.

[0015] According to the present invention in another aspect thereof,there is provided a method of metal plating an article having a boreprovided therein, wherein the article is masked for plating bypositioning a sealing member such that it extends through the bore andacts to seal the bore, substantially preventing plating fluid fromentering therein, the sealing member being a length of foam which iscompressed and passed through the bore of the article to seal the bore,a conductive wire being passed through the bore with the foam and beingpositioned so as to be in contact with the article, to enable a currentto flow through the article during electroplating.

[0016] The foam is preferably impermeable, and advantageously expands onheating. The foam may be expanded polyethylene cord. Preferably the foamhas a diameter larger than that of the bore before compression. The foamis preferably heated before the electroplating process such that thefoam expands and provides an effective seal to prevent liquid fromentering the bore.

[0017] According to the present invention in another aspect thereofthere is provided a method of metal plating an article wherein thearticle is masked for plating by positioning a sealing member such thatit is in close contact with a part of the article and acts to seal offthat part of the article, substantially preventing plating fluid fromtouching that sealed off part of the article, and wherein the article isfirmly held in position against the sealing member by a force exertingdevice.

[0018] The sealing member may be located on a frame. Preferably theforce exerting device is provided on the frame for allowing an articleto be held firmly adjacent the sealing member. When the article isfirmly held in the frame, at least part of the frame, and the articleare exposed to a metallic solution. The frame is advantageously capableof conducting current, such that the current flows through the articleheld in the frame. The article is preferably dipped, whilst held in theframe, in a metallic solution. As the article is dipped in the metallicsolution a current flows through the article and causes the article tobecome metal plated. Cadmium may be present in the solution so that thearticle becomes plated in cadmium.

[0019] Several examples of the present invention will now be describedby way of example only and with reference to the following drawings:

[0020]FIG. 1 shows a side elevation view of an example of the presentinvention;

[0021]FIG. 2 shows a side elevation view of a second example;

[0022]FIG. 3 shows a side elevation view of a third example; and

[0023]FIG. 4 shows a side elevation view of a fourth example,

[0024]FIG. 5 shows an isometric view of a fifth example.

[0025]FIG. 1 shows three bushes 1, 3, 5 threaded onto a length of foam7, and a copper wire 9. The foam 7 is impermeable, expands on heating,and has a greater cross-sectional area than the bore of each of thebushes. The foam 7 is compressible such that it may be pushed throughthe bore of each bush.

[0026] The copper wire 9 is slid through the bore of each bush with thefoam 7, so that the copper wire touches the bush.

[0027] The foam is then heated so that it expands and provides aneffective seal 11 preventing seepage of liquid into the bore of eachbush.

[0028] The bushes are then suspended in a cadmium solution from thecopper wire, and a current is passed through the copper wire, causingthe exposed surfaces of the bush to become cadmium plated. The cadmiumsolution is prevented from entering the bore by seal 11 and so the boredoes not become cadmium plated.

[0029]FIG. 2 shows a bush 13 having a bore 15. The bush is positioned ona ball 17 that is welded to a frame 19. A second ball 21 rests on thebush 13 at the opposite end to ball 17. The ball 21 is connected to theframe 19 by a spring 23, the spring 23 exerting a force on ball 21 inthe direction indicated by arrow A to cause the bush 13 to be firmlyheld in the position shown between balls 17 and 21.

[0030] A portion 25 of ball 21 extends into one end of the bore 15 and aportion 27 of ball 17 extends into the other end of bore 15. Thepressure exerted by spring 23 causes the balls 21, 17 to effectivelyseal the bore 15, preventing liquid from entering therein.

[0031] The frame 19 is made from an electrically conductive materialcoated in an insulator such as a plastic material. The frame hascontacts 29, 31 for allowing a current to flow from an electrical source(not shown) through the core conductive material in the frame. Thespring 23 preferably has a conductive core coated in a non-conductivematerial for allowing current to flow through the spring and into theball 21. Balls 21 and 17 are preferably made from titanium, so that theycan conduct current into the bush 13 without themselves becoming cadmiumplated. Alternatively, the balls 17 and 21 may be made from steel coatedwith a nonconductive material such as plastic, the plastic being cutaway at the point where the ball makes contact with the bore 15.

[0032] In use, the frame 19 holding the bush 13 is dipped into a cadmiumsolution and contacts 31 and 29 are connected to an electrical source sothat a current is passed through the frame 19, the current flowingthrough the spring 23, balls 21 and 17 and the bush 13. The exposedsurfaces of the bush become cadmium plated, but the balls 21, 17 preventcadmium solution from entering the bore 15 and so the bore does notbecome cadmium plated.

[0033] This embodiment allows numerous bushes to be platedsimultaneously, as a frame can be constructed having several ballswelded or otherwise fixed to the frame, and several spring loaded ballsattached to the frame above or adjacent the first balls to provideseveral pairs of balls for holding bushes on a single frame.

[0034]FIG. 3 shows part of a frame 19, the frame being constructed asdescribed with reference to FIG. 2. A frustum 33 is fixed to the frame19 as shown, so that the larger end 35 of the frustum 33 is in contactwith frame 35 and the narrow end 37 is free to receive a bush 39 havinga bore 41. A second frustum 43 is attached to frame 19 by a spring 23,the spring being similar to that described with reference to FIG. 2.

[0035] The frustums 33, 43 may be made from a conductive material whichis coated in a compressible insulator, for example steel coated withrubber or a compressible plastic material. Alternatively the frustums33, 43 may be made from a non-conductive material which is to an extentcompressible, such that the frustums 33, 43 an be inserted and wedgedinto the bore 41 of a bush 39, providing a seal to prevent liquid fromentering the bore 41.

[0036] The frustum 33 has an electrically conductive wire or spring 45running through it for electronically connecting the inner annularsurface 47 of the bush to the frame 19.

[0037] In use, the bush is placed on frustum 33 and manually pushed sothat the end 37 of frustum 33 extends as far as possible into the bore41. The second frustum 43 is then positioned so that the narrow end 49of frustum 43 extends as far as possible into the other end of the bore41, as shown in FIG. 3. Frustum 43 is kept firmly in position by spring23, which exerts a force in the direction indicated by arrow B.

[0038] The frame 19 is connected to an electrical source as describedwith reference to FIG. 2 and the frame 19 is then placed in a bath ofcadmium solution. An electrical current is passed through the frame, thecurrent flowing through the spring or wire 45 to the bush 39. The bush39 becomes plated in cadmium, except for the bore, as the cadmiumsolution is prevented from entering the bore due to the frustums 33, 43.

[0039] In this embodiment, spring 23 does not need to conduct current.An advantage of this embodiment is that bushes of various bore sizes maybe accommodated on one size of frustum. This reduces the need forfrustums of various sizes, and so is more cost effective. The frame 19may comprise several pairs of frustums attached thereto as shown.

[0040]FIG. 4 shows the same apparatus as that of FIG. 3, except thearticle 51 to be cadmium plated has a recess 53 rather than a boreextending through the article. The article 51 is positioned on frustum33 such that the narrow end 37 of frustum 33 extends as far as possibleinto the recess 53. The electronically conductive spring or wire 45extends from the frame 19 through the frustum 33 to make contact withthe surface 55 of the recess 53. Frustum 43 is then positioned adjacentthe article 51 as shown, and the spring 23 exerts a force in thedirection shown by arrow B to clamp the article 51 in position duringthe cadmium plating process which is as described with reference to FIG.3. FIG. 5 shows part of a frame 19, the frame being constructed asdescribed with reference to FIG. 2. A resilient member 57 is connectedto the frame, and a ball 59 is attached to the resilient member 57. Aplate 61 is attached to the frame 19. The plate 61 is incompressible andpreferably coated with a nonconductive material, except for anelectrically conductive portion for making contact with an articlepressed against the plate. Alternatively, the plate could be made fromtitanium. In use, a flat topped bush 63 is placed against the plate 61such that the flat end of the bush 63 makes contact with theelectrically conductive portion of the plate 61. The ball 59 is placedso that it extends into the bore 65 of the bush 63 at the end remotefrom the flat end, and the ball 59 is tightly held in position by theresilient member 57, effectively sealing the bore 65 of the bush 63 andpreventing liquid from entering therein during plating. The ball 59 ispreferably made from titanium, or alternatively steel coated with anon-conductive material except at the locations where the ball 59 makescontact with the bore 65. The resilient member 57 has a conductive corecoated in a non-conductive material, for allowing current to flow fromthe frame 19, through the resilient member 57, and into the ball 59. Theflat top will not become plated if the plate 61 is in close contact withthe whole of the top, thereby preventing plating liquid from touchingthe top of the bush.

[0041] Articles having a bore and flat top may be treated in thismanner, as well as articles having a recess and flat top. The plate mayalso be used in this manner for masking regions of a substantiallyplanar surface of an article.

[0042] It will be recognised that various modifications of thisinvention may now suggest themselves to a person skilled in the art,without departing from the essence of this invention.

1. A frame having a plurality of sealing members positioned thereon, theframe being capable of conducting an electrical current between sealingmembers, each sealing member being adapted to be in close contact withpart of an article to be located thereon and to thereby substantiallyprevent fluid from touching that part of the article or entering into abore or recess of the article, each sealing member further being adaptedto conduct current between the frame and the article.
 2. A frame asclaimed in claim 1 wherein a force exerting device is provided on theframe for exerting a force on the article to hold the article firmly inclose contact with a sealing member.
 3. A frame as claimed in claim 2wherein the force exerting device comprises a resiliently biased member.4. A frame as claimed in any of claims 1 to 3 wherein the sealingmembers are substantially planar.
 5. A frame as claimed in any of claims1 to 3 wherein the sealing members are adapted to extend at least partway into a recess or bore of the article to be located thereon.
 6. Aframe as claimed in any preceding claim wherein the force exertingdevice is adapted to hold the article between two sealing members.
 7. Aframe as claimed in any of claims 1 to 5 wherein the force exertingdevice is adapted to hold the article between the force exerting deviceand a sealing member.
 8. A frame as claimed in any of claims 1 to 7wherein the sealing members are formed from a compressible,non-conductive material.
 9. A frame as claimed in any of claims 1 to 7wherein the sealing members comprise an electrically conductive coresubstantially encased in an electrical insulator material.
 10. A frameas claimed in any preceding claim wherein an electrically conductivemember extends from the frame through a sealing member such that theelectrically conductive member is capable of forming an electricalcontact between an article located on the sealing member, and the frame.11. A frame as claimed in any of claims 1 to 7 wherein the sealingmembers are formed from titanium.
 12. A frame as claimed in anypreceding claim wherein the frame is coated in a non-conductive materialto prevent the frame from becoming metal plated when a current isapplied to the frame and it is exposed to a metallic solution.
 13. Aframe having a plurality of sealing members positioned thereon, theframe being capable of conducting an electrical current between sealingmembers, each sealing member being adapted to extend at least part wayinto a recess or bore of an article to be located thereon and tosubstantially prevent fluid from entering into the bore or recess of thearticle, each sealing member further being adapted to conduct currentbetween the frame and the article.
 14. A method of metal plating anarticle having a bore provided therein, wherein the article is maskedfor plating by positioning a sealing member such that it extends throughthe bore and acts to seal the bore, substantially preventing platingfluid from entering therein, the sealing member being a length of foamwhich is compressed and passed through the bore of the article to sealthe bore, and wherein a conductive wire is passed through the bore withthe foam and is positioned so as to be in contact with the article, toenable a current to flow through the article during electro-plating. 15.A method of metal plating an article as claimed in claim 13 wherein thefoam is heated before the electroplating process such that the foamexpands and provides an effective seal to prevent liquid from enteringthe bore.
 16. A method of metal plating an article wherein the articleis masked for plating by positioning a sealing member such that it is inclose contact with a part of the article and acts to seal off that partof the article, substantially preventing plating fluid from touchingthat sealed off part of the article, and wherein the article is firmlyheld in position against the sealing member by a force exerting device.